Evaporation caps are known for incubator stations on a rotor. Examples are disclosed, e.g., U.S. Pat. No. 4,963,333. The caps so disclosed feature camming feet at two of four corners of the cap, and two pivot feet at the other two corners. A recess is provided in the undersurfaces to accommodate two upwardly projecting liquid drops on a potentiometric slide element. The cap works by pivoting on its two pivot feed due to the camming feet riding up onto an incoming slide, thus clearing the cap undersurface from contact with the upwardly projecting drops.
Such a cap works well when the location of the upwardly projecting drops is adjacent the trailing edge of the slide element, such as is the case on the analyzer available from Eastman Kodak Company under the trademark "Ektachem 250", hereinafter the "E-250". It does not work so well, however, if the slide element is turned 180.degree. so that the upwardly projecting drops are adjacent the leading edge of an incoming slide element. The latter occurs when using a slide distributor such as is found in the analyzer disclosed in U.S. Pat. No. 4,298,571. Distributors are particularly useful when using more than 1 incubator, e.g., as in the "Ektachem 700".TM. analyzer also available from Eastman Kodak Co. That distributor receives the slide in the orientation mentioned for the "E-250", and then turns it 180.degree. for insertion into an incubator. Such a distributor is not used on the E-250. The reason why the 180.degree. reversal of the slide renders the described cap less useful is that the resulting nearness of the projecting drops to the pivot edge of the cap necessitates a larger size of the camming feet that is impractical.
However, because a single incubator cannot be made indefinitely large, then such a distributor allows for a higher throughput, using plural incubators, than when it is not used. It would be advantageous to provide a cap that cams upwardly by some mechanism as the potentiometric slide enters with the upwardly-projecting drops adjacent the leading edge. Such camming has to be done with some care, since the upwardly-projecting drops should not be jarred sideways, that is, along the axis connecting them, lest the needed flow of the drops towards each other to form a junction, be disturbed.
It is this need that, prior to this invention, has not been achieved inexpensively, by a design allowing ready access to top removal of the caps for cleaning and the like.